and they don’t play back as they ought to.
Sorry for bumping (I know how you feel about it) but after one week I think you might have missed what might be a bug, grace notes gets corrupted when doubling note duration. They seem to stay in the same place and they don’t play back well.
That is indeed a known problem, grace notes not moving along if earlier notes change duration with insert mode enabled. It’s not completely trivial to fix, but we are certainly planning to improve this in a future update.